The present invention generally relates to a transmission power control method and apparatus for mobile communication system which controls the transmission power between the base station and mobile terminal of a mobile communication system, and particularly to the effective technology suitable for use in the transmission power control method and apparatus for mobile communication system which controls the transmission power in accordance with the change of signals received between the base station and mobile terminal of the mobile communication systems such as TDD-SS (Time Division Duplex-Spread Spectrum) and FDD (Frequency Division Duplex) systems.
There is a conventional mobile communication system for transmitting and receiving data by radio between base stations and mobile terminals. This mobile communication system employs different carrier frequencies for the up link on which signals are transmitted from a mobile terminal to the base station and for the down link on which signals are transmitted from the base station to the mobile terminal by, for example.
The signal transmitted and received between the base station and mobile terminal of this mobile communication system is attenuated along the distance between the base station and mobile terminal, and by obstacles present therebetween, and fluctuated by the fading due to the interference between the direct wave and the reflected wave, or the like.
In order to compensate the fluctuation due to the fading in the signal transmitted and received between the base station and the mobile terminal which is dependent upon the carrier frequency, the transmission power in the FDD mobile communication system is controlled by closed-loop control. For example, the IS-95 specifications apply up link transmission power control of the FDD system which controls the transmission power of the terminal. The technique on the scheme of the FDD down link power control is proposed in U.S. Pat. No. 5,559,790 entitled "Spread Spectrum Communication System and Transmission Power Control Method Therefore" invented by Yano, et al., assigned to the present assignee and issued Sep. 24, 1996. In addition, another technique on the information of the up link power control is proposed in a copending U.S. patent application Ser. No. 08/690,819 entitled "CDMA Mobile Communication System and Communication Method" by those inventors, assigned to the present assignee and filed on Aug. 1, 1996. The disclosure of the above U.S. Application, and the continuation application, Ser. No. 08/678,656 of the above U.S. patent, filed on Jul. 11, 1996, are incorporated in the disclosure of this application by reference.
Whether the mobile communication system is of CDMA-FDD or CDMA-TDD, the following problem is caused when transmission power control is performed through the transmission path between the mobile terminal and the base station. In other words, when the attenuation of data in the transmission path between the base station and a particular mobile terminal is temporarily increased, the base station transmits signals with an extremely higher power in accordance with the transmission power control, and thus interferes with other mobile terminals. In addition, when the transmission power from a mobile terminal, on the contrary, is excessively risen, it also obstructs or interferes with other base stations.
Moreover, in the FDD mobile communication system, since the closed loop control is still performed in which the transmission power on the up link is controlled by the mobile terminal in accordance with the up link power control information obtained at the base station, while that on the down link is controlled by the base station in accordance with the down link power control information attained at the mobile terminal, there is the problem that it takes a long time to control the transmission power.